Abstract/Summary

The long-term North Atlantic Cold Anomaly (Cold Blob, CB) was largely defined by three major episodes of low sea surface temperature (SST) in the subpolar North Atlantic in 1972–1974, 1984–1985 and 1991–1994. Without these cold periods, there would have been no CB. Each of these episodes correlated with unusually low SST at the Flemish Cap (a subsurface island of the Canadian continental shelf) and with periods of high sea ice cover over the deep basin of the Labrador Sea a year earlier. These cold periods at the Flemish Cap and the CB were associated with the advance of sea ice and icebergs to the Flemish Cap, high iceberg counts off the coast of Newfoundland and the encroachment of icebergs on the path of the North Atlantic Current (NAC). Studies of SST anomalies in high iceberg years provided evidence for surface connections between the Flemish Cap and the CB utilizing part of the NAC pathway. We propose that in the cold periods, residual meltwater from sea ice and icebergs conveyed in the Labrador Current to the Flemish Cap was relayed via the NAC to the subpolar North Atlantic to form the CB. After 1995, anomalous ice expansion in the Labrador Sea basin greatly diminished, sea ice and icebergs did not reach the Flemish Cap and cold meltwater was no longer transmitted to the subpolar North Atlantic to sustain the CB. These observations make it difficult to see how the CB could be relevant to mooted changes in the Atlantic Meridional Overturning Circulation and associated impacts on regional climate in the twenty-first century.